I cant believe folks think spanking (light or not) achieves anything. All that spanking reinforces is ... its ok to lose your temper, it is ok to hit when you lose your temper.
Make no mistake, even the youngest children realise that you are spanking because you are upset, not so much because you want the child to understand and follow good behavior. The pain hurts thier butt, but it also tells them that this adult who hit me cannot be in control of themselves. Dosent do much for the respect they will have for your actions in the long run.
Give the child a time out. Really it is not so much the child who needs the time out, it is the adult who needs it regain composure and then be reasonable about showing the child that actions have consequences. Within reason, take away a privilege, take away a toy, something that actually affects the child.
Adults who hit should work on thier anger management skills first before discipling anyone else.
This child has had huge upheavals. Daycare, siblings etc. He is also testing his boundries. It is natural part of the awareness and growing process. If he didnt make mistakes, and tested his boundries he would never learn. So he is not doing it to piss you off as much as he is doing something that is part of his development.